Method of recovering cyanids.



No. 689,0!8. Patented Dec. l7, [90L W. 0BR.

METHOD OF BEDOVEBING GYANIDS.

(Application filed Hat. 5, 1901.)

(No Model.)

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UNITED States smear Orricn.

WILLIAM ORR, OF SALT LAKE CITY, UTAH, ASSIGNOR TO THE GOLD AND SILVEREXTRACTION COMPANY OF AMERICA, LTD., OF DENVER, COLO- RADO, AJOINT-STOCK COMPANY OF GREAT BRITAIN.

METHOD OF RECOVERING CYANIDS.

SPECIFICATION forming part of Letters Patent No. 689,018, dated December17, 1901.

' Application filed March 5, 1901. Serial No. 49,794. (No specimens.)

To all whom it may concern:

Be it known that I, WILLIAM ORR, a subject of the Queen of GreatBritain, residing in Salt Lake City, State of Utah, have invented cer-.

tain new and useful improvements in methods of and processesfor'recovering cyanids of potassium or sodium from cyanid solutionsfouled by the presence of double cyanids of zinc and copper With thealkali metals, of

which the following is a full, clear, concise,

and exact description,sufficient to enable persons skilled in the art towhich it appertains to use the same.

My present invention relates to the regeneration of those solutions ofcyanid which have become, as it is called, fouled while being used inthe now well-understood process of extracting precious metals from oresor tailings by the formation therein of double cy- 2o anids of otherthan the precious metals-as,

for instance, double cyanids of zinc and copper with potassium, sodium,or other alkaline metals. Certain ores and tailings bearing preciousmetals which it is desired to extract therefrom by the said cyanidprocess of extraction contain, on the one hand, considerable quantitiesof copper, which during the application of the said process combine withthe cyanid of potassium or sodium employed as the solvent to form adouble cyanid of copper and potassium or sodium. On the other hand, thezinc made use of at one stage of the process for the purpose ofprecipitating the precious metals likewise combines to a con- 5siderable extent with the said cyanids of potassium and sodium to formin the solution the double cyanid of zinc and potassium or sodium. Inthe third place, certain of the ores or tailings treated as aforesaidcontain.

also zinc minerals, the zinc of which also tends in many instances tosimilarly combine with the said cyanids of the solution to produce anadditional quantity of the double cyanid of zinc and potassium orsodium. The presence of these double cyanids in the solution constitutesalways an obstacle or disadvantage to the solvent efficiency thereof inits relation to the precious metals, for not only is thereby withdrawnfrom active use in the solution a considerable proportion of the saidcyanids ofpotassium or sodium, which otherwise would act directly assolvents of the precious metals, but the said double cyanids alsoconstitute an addition of inert matter in the solution unavailable for.the purpose of extracting the precious metals and positively injuriousin that they proportionately impair the capacity of the solution forabsorbing oxygen, the latter element being essential to the solution ofthe precious metals in the cyanid solution. Besides this, the presenceof the copper in the solution interferes to a serious extent in theprecipitating of the precious metals when zinc is used as theprecipitant, the copper tending to become deposited to a slight extentupon the zinc, thus coating it and preventing the latter from cominginto the proper contact with the precious metals held in the solution.For these and other reasons it has long been sought to devise someindustrially economical method of removing from the solution the saidcopper and the said zinc thus held in the double cy anidsof those metalswith the alkali metals. In solutions thus fouled or infected by thepresence of these undesirable compounds it is impossible to precipitateand separate the said zinc therefrom by methods invented by me andapplicable to cases in which the ores or tailings are substantially freefrom copper, because, as I have discovered, the said double cyanids ofcopper and ofzinc With the alkali metals combine together, so as toresist any alkaline hydrate and sulfid treatment.

The object of my present invention, therefore, is to produce a simple,economical, and industrially applicable method or process for removingfrom the said oyanid solutions employed as aforesaid the said injuriouscompounds of copper or zinc with alkaline cyanids. I obtain this objectby the application of the process which I will now describe, making usetherein, among others unnecessary to be specifically described for a.full understan ding of my invention, of certain apparatus illustrated inthe accompanying drawings, in which Figure 1 represents a plan or topview (cover A being removed) of my copper-precipitating apparatus; Fig.2, a central vertical longitu- ICO vertical section taken on the linewas of Fig. 1.

Similar letters in each drawing indicate similar parts.

I provide a box 13 of any suitable form or construction adapted to thepassage therethrough of the solution which it is required to treat by mysaid process. 'Within this box I support a series of copper plates 0 c,electrically connected with each other by conductors m m and with asource of negative electricity. Intermediate between the said copperplates I likewise-support a corresponding series of zinc plates ,2 .2,likewise electrically connected together by conductors n n and with asource of positive electricity. The said solution containing the saidundesirable compounds of zinc and copper is caused to flow through thisbox in any convenient manner, entering, for instance, by the aperture Oand passing out by the aperture D. The solution is thus caused to passaround and between the aforesaid plates, and a current of electricity issimultaneously passed through thela-tter and the solution, as indicated.The electrical action decomposes the aforesaid compound of copper in thesolut ion and causes the metallic copper to be deposited upon the copperplates or cathodes, while the liberated cyanogen attacks the zinc anodesand combines therewith to produce additional double cyanids of zinc andpotassium or sodium in the solution. The solution during its passagethrough the box, as aforesaid, is thus deprived of its copper, the placeof the double cyanid ofcopper and potassium or sodium being taken by anequivalent of the double cyanid of zinc and potassium or sodium. I nexttie it in the following manner the said solution so deprived of itscopper: I transfer the solution to any convenient and suitable tank orreservoir and retainingit temporarily there, I add thereto a certainamount of alkaline hydrate-for instance, preferably, sodium hydrate,potassium hydrate, calcium hydrate, or barium hydrate or a combinationof'two or more of these.

In the ordinary course of practice it is not usually required ordesirable to release all of the cyanid held up in combination as thedouble cyanid of zinc and potassium or sodium, the presence of zinc inthe solution being much less detrimental than copper toits effioiencyfor the purpose of extracting the precious metals, and while by the useof my process it is entirely possible, if required, to release all ofthe cyanid so held up, a moderate proportion thereof is usually allthatis requiredto restore the solution to its original strength. Theamount of said hydrate to be added to the solution will depend,therefore, upon the extent to which it is desired to regenerate itssolvent strength. For instance, assuming that in a ton of cyanidsolution fifty pounds of the cyanid is held up in the form of doublecyanid of zinc and potassium and that the solvent efficiency of thesolution in relation to that particular extraction of precious metalsfor which it is employed requires the restoration of eight pounds offree cyanid of potassium. In such a case the amount of hydrate addedshould be sufficient to secure the disassociation of a sufficientquantity of the double cyanid of zinc and potassium to insure thereafterthe complete combination with the zinc of all the sulfid added, ashereinafter described.

The reaction produced by the introduction of the aforesaid hydrates maybe exemplified as follows: For instance, where a sodium hydrate is used,illustrating the action of the monovalent alkali metals,

or where calcium hydrate is used, illustrating the action of thedivalent alkaline earth metals,

l find in the ordinary practical application of my invention to millsolutions requiring regeneration to a certain point of efficiency, asaforesaid, that the amount of alkaline hydrate introduced willapproximate .l per cent. or, say, two pounds per ton of solution, thisproportion being of course, however, subject to increase should it berequired to recover a larger percentage of free cyanid, as likewise incases in which the solution is found to give an acid reaction. Accordingto the various conditions presented by each case of different ores ortailings bringinginto the solution certain elements and ingredients,different alkaline hydrates, including hydrates of one of thealkaline-earth metals, or diiferent combinations of two or more of thesemay be used with efficiency, depending upon the particular conditionspresented by each case, and it is therefore desirable to determine byactual laboratory tests in each instance the particular hydrate or h ydrates best adapted for the particular purpose and occasion in hand.Taking, however, the case of a solution from which the copper has beenremoved, as aforesaid, and which presents no new or extraordinaryfeaturessay the average dilute cyanid solution-and which contains atthis point in the application of my process, say, fifty pounds per tonof cyanid, held up in the said double cyanid of zinc and potassium andonly four pounds remaining 'of free cyanid of potassium, I find that onits being required to raise the strength of such a solution in saidcyanid of potassium to, say, twelve pounds per ton, the desired resultcan be successfully accomplished through the use of my method by theaddition to the said solution of from two to three pounds per ton of thesaid hydrates, preferably, say, about two pounds of sodium and one poundof calcium hydrate to each ton of the solutionn Having added the hydrateto the solution, as afore- IIO said, 1 next mix thoroughly, so as toinsure as far as possible the disassociation of the double cyanid ofzinc and potassium into a zincate and free cyanid of the alkali.

The next step in my process is to introduce into the solution treated asaforesaid an amount of an alkaline sulfid or sulfid of one of thealkaline-earth metals (preferably fused sodium sulfid sixty-five percent. Na s) in amount somewhat less than required to precipitate allthezincate produced, as aforesaid, it being important to insure that nosoluble sulfid shall be left unprecipitated in the solution. The effectof the introduction of the sulfid, as aforesaid, is to precipitate thezinc as zinc sulfid, which may afterward be separated in any convenientmanner, either by decantation or by filtration through a .filterpress.The filtered or supernatant liquor contains the cyanid which wasformerly in combination with the zinc and which now appears as freepotassium cyanid, rendered again available for further solution of theprecious metals or other economic uses. It is of essential importancethat the aforesaid hydrate should be added before the introduction ofthe sulfid and appreciablyin advance thereof. Other- Wise a completereaction between the zinc salt and the soluble sulfid will be impossibleand the solution correspondingly damaged rather than benefited by theintroduction of the latter. The reaction in the solution resulting fromthe introduction therein, as aforesaid, of the sulfid may be expressedby the following formula:

The amount of soluble sulfid thus introduced will vary in each caseaccording to the requirements within the limitations above describedthatis to say, in no case should the amount of the sulfid exceed thatrequired to precipitate all the zincate in the solution, and it isimportant,therefore, to introduce in every instance less of the solublesulfid than is required to precipitate all of such zincate.

In cases Where two or three pounds per ton of alkaline hydrates havebeen introduced into the solution, as aforesaid, I have obtained resultsentirely satisfactory by the subsequent introduction therein, asaforesaid, of from .08 to .1 per cent. of fused sodium sulfid.

Having thus described my invention, what I claim as new, and desire tosecure by Letters Patent, is the following, viz:

1. The method of regenerating cyanid solutions which have become fouledby the presence of zinc and copper contained in the solution as thedouble cyanids of zinc and copper with the alkali metals, which consist,first, in passing through the solution from a series of zinc anodes to acorresponding series of metallic cathodes, a current of electricity,next, in introducing into the solution alkaline hydrate, next inintroducing into the said so lution, so treated, a soluble alkali-metalsulfid, and finally in separating from the solution the resultingzinc-sulfid precipitate substantially as and for the purposes described.

2. The method of regenerating cyanid solutions which have become fouledby the presence of zinc and copper contained in the solution as thedouble cyanids of zinc and copper with the alkali metals, whichconsists, first in passing through the solution from a series of zincanodes to a corresponding series of copper cathodes a current ofelectricity, next in introducing into the solution alkaline hydrate,next in introducing into the said solution, so treated, a solublealkali-metal sulfid and finally in separating from the solution theresulting zinc-sulfid precipitate, substantially as and for the purposesdescribed.

3. The method of regenerating cyanid solutions which have become fouledby the presence of zinc and copper contained in the solution as doublecyanids of zinc and copper with the alkali metals which consistsfirst,in passing through the solution from a series of zinc anodes to acorresponding series of copper cathodes a current of electricity, nextin introducing into such solution hydrates of so dium and calcium inproportions of about two to onefnext introducing into the solution asoluble alkali-metal sulfid and finally removing the resultingzinc-sulfid precipitate, sub stantially as and for the purposesdescribed.

t. The method of regenerating cyanid solutions which have become fouledby the presence of zinc and copper contained in the solution as doublecyanids of zinc and copper with the alkaline metals which consistsfirst,

in passing through the solution from a series of zinc anodes to acorresponding series of metallic cathodes a current of electricity, nextin introducing into such solution hydrates of sodium and calcium inproportions of about two to one,next introducing into the solution asoluble alkali-metal sulfid and finally removing the resultingzinc-sulfid precipitate, substantially as and for the purposesdescribed.

5. The method of regenerating cyanid solutions which have become fouledby the presence of zinc and copper contained in the so-' lutions asdouble cyanid of zinc and copper with the alkaline metals which consistsfirst, in passing through the solution from a series of zinc anodes to acorresponding series of metallic cathodes a current of electricit-y,nextin introducing into such solution, alkaline hydrate being hydrate of themonovalent alkali metals and hydrate of the divalent alkali metals inthe proportions of about two to one, next introducing into the solutiona soluble alkali-metal sulfid and finally removing the resultingzinc-sulfid precipitate, substantially as and for the purposesdescribed.

'WILLIAM ORR. Witnesses:

WALTER D. EDMoNDs, GEo. G. Munsunns.

